<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <script>
        const arr = [
            { id: 1, name: 'melon', state: true , price: 10, count: 2},
            { id: 1, name: 'melon', state: false,  price: 30, count: 1},
            { id: 1, name: 'melon', state: true,  price: 10, count: 1}
        ]

        // let amt = 0
        // arr.filter(item => item.state).forEach((item) => {
        //     amt += item.price * item.count
        // })
        // console.log(amt)

        // arr.filter(item => item.state).reduce((累加的结果，当前循环项) => { }, 初始值)

        const result = arr.filter(item => item.state).reduce((amt, item) => {
            return amt += item.price * item.count
        }, 0)

        console.log(result)

    </script>
</body>
</html>